1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, a semiconductor device having an internal power supply voltage generation circuit.
2. Description of the Background Art
Some of semiconductor devices are provided with various kinds of internal power supply voltage generation circuits for generating a voltage level different from an external power supply voltage applied to an internal circuit from the outside of the semiconductor device by using the external power supply voltage. In recent years, while demanded is a circuit structure with an operation voltage lowered in order to reduce power consumption, because a required operation voltage level varies according to the purpose of use, also demanded is provision of an internal power supply voltage generation circuit which generates a higher voltage level as compared with an external power supply voltage, for example, a booster circuit.
Circuit structure of a booster circuit includes, for example, a constant voltage generation circuit for outputting a reference voltage whose level is fixed independently of an external power supply voltage, a pump circuit for generating a boosted voltage level, a shifter for shifting a boosted voltage level by a certain rate, and a sensing circuit for comparing an output of the shifter and an output of the constant voltage generation circuit to control pumping operation so as to maintain a boosted voltage level at a desired value based on the comparison result.
In addition, Japanese Patent Laying-Open No. 2004-63019 discloses a booster circuit which reduces power consumption at the time of stand-by of an internal power supply voltage generation circuit in a semiconductor storage device. Japanese Patent Laying-Open No. 2004-280923 discloses a booster circuit with suppressed effects of temperature dependency and threshold voltage dependency of an internal power supply voltage generation circuit.
In these circuits, however, when an external power supply voltage is at a level not more than a target voltage level, as a boosted voltage level, because it is increased with an increase in the voltage level of the external power supply voltage, only a voltage level extremely lower than the maximum output level of the pump circuit can be output. In other words, when the external power supply voltage is a low voltage, the maximum output level of the pump circuit and an output level of the constant voltage generation circuit might be close to each other or inverted.
While the sensing circuit continues outputting an activation signal to instruct on pumping operation when determining that a boosted voltage level is low, when the external power supply voltage is a low voltage, because the pump circuit has no output which obtains such a level as inactivates an activation signal of the sensing circuit, it will be instructed to execute pumping operation all the time.
As a result, characteristics that power consumption of the pump circuit is increased will be obtained.
Although in particular, when the voltage level of the external power supply voltage is high as an operation voltage guaranteed by the device, this increase of power consumption is not a great problem, the lower the voltage level of the external power supply voltage becomes, the greater the effect on the device exerted by the increase in power consumption will be to pose a problem.